In the oil and gas industry, hydrocarbon reservoirs have conventionally been accessed by vertical or near-vertical wellbores. Such reservoirs, however, are increasingly accessed via non-vertical wellbores.
Tools that have conventionally been used in the vertical or near-vertical wellbores may encounter problems when used in the non-vertical wellbores. Such tools may be lowered into wellbores as part of a tool string utilizing gravity to facilitate transport or movement therethrough. In non-vertical wellbores, gravity may be negated by frictional forces between the tool string and walls of the wellbore, thus resisting movement of the tool string through the wellbore. Furthermore, particularly with open-hole wellbores not lined with casing, outer surfaces of the tool string may stick to the wall of the wellbore, or edges of the tool string may dig into or jam against imperfections in the wall of the wellbore.
In addition to the increased friction due to an increased horizontal gradient, the movement of the tool string along the non-vertical wellbores may be impeded further by the presence of various obstacles. For example, washouts, sharp bends, misaligned tubular joins, transitions between lining, casing, and bare walls of the wellbore, and other uneven surfaces may present an increased resistance or impediments to the movement of the tool string through the wellbore.